Hearing devices are wearable hearing apparatus used to assist the hard-of-hearing. To meet the numerous individual requirements different designs of hearing device are provided, such as behind-the ear (BTE) hearing devices, in-the-ear (ITE) hearing devices and Concha hearing devices. The typical configurations of hearing device are worn on the outer ear or in the auditory canal. Above and beyond these designs however there are also bone conduction hearing aids, implantable or vibro-tactile hearing aids available on the market. In such hearing aids the damaged hearing is simulated either mechanically or electrically.
Hearing devices principally have as their main components an input converter, an amplifier and an output converter. The input converter is as a rule a sound receiver, e.g. a microphone, and/or an electromagnetic receiver, e.g. an induction coil. The output converter is mostly implemented as an electroacoustic converter, e.g. a miniature loudspeaker or as an electromechanical converter, e.g. bone conduction earpiece. The amplifier is usually integrated into a signal processing unit. This basic structure is shown in FIG. 1 using a behind-the ear hearing device as an example. One or more microphones 2 for recording the sound from the surroundings are built into a hearing device housing 1 worn behind the ear. A signal processing unit 3, which is also integrated into the hearing device housing 1, processes the microphone signals and amplifies them. The output signal of the signal processing unit 3 is transmitted to a loudspeaker or earpiece 4 which outputs an acoustic signal. The sound is transmitted, if necessary via a sound tube which is fixed with an otoplastic in the auditory canal, to the hearing device wearer's eardrum. The power is supplied to the hearing device and especially to the signal processing unit 3 by a battery 5 also integrated into the bearing device housing 1.
When inductive transmission systems are used in hearing aid devices it is necessary to keep down the influence of internal faults, i.e. those generated in the hearing aid device itself. Electromagnetic interference signals which are created within the hearing aid device, impose a load on the receive path of the transmission system, so that only those external signals are received for which the signal strength is above the signal strength of the interference signals.
Typical sources of electromagnetic interference are for example the earpiece, which is embodied as a magnetic converter, or the hearing aid electronics, which itself emits electromagnetic interference signals. In addition all connecting lines between the components of the hearing aid device which, from the current flow through the lines, function as inductive antennas should be mentioned as sources of interference. The overlaying of these numerous electromagnetic interference signals emitted by the different interference sources will be received at the location of a receive antenna or of a receive coil of a wireless signal transmission system which uses the inductive range or the typical HF range.
Assuming that the local arrangement of all components in a hearing aid device is fixed line loops can be deliberately applied through which a current flows and which generate the corresponding opposing field at the location of the receive antenna. A corresponding hearing aid device with a line loop to compensate for inductive interference fields is known from patent application DE 10 2004 051 226 B3. In concrete terms it is proposed in this document to lay a line loop such that its axis runs in parallel to that of a send/receive coil. Compensation for inductive interference fields has the disadvantage however that the size of the interference fields must at least be known as regards their order of magnitude. A further disadvantage of this line laying arrangement lies in the fact that the line can be squashed, scraped or nicked when the hearing device is closed. In addition this line laying arrangement requires sufficient space, around the battery of the hearing device for example.
Different forms of antennas extending in one plane are described in WO 2005/081583 A1. The antennas are fitted in a hearing device so that as much of their surface area as possible touches a battery of the hearing device. In this way the battery shields the antenna from electromagnetic radiation which is emitted by other components of the hearing device, for example by the loudspeaker.